Modern aircraft wings often include a series of movable flight control surfaces, such as flaps or slats that can be selectively extended or retracted to modify the lift producing characteristics of the wings. Extension and retraction of such flaps or slats is accomplished by a flight control actuation system mounted in the wing.
A typical actuation system includes a series of actuators spaced along the span of each wing, and operably connected to move one or more individual flight control surfaces. Adjacent actuators are connected to each other by drive shafts to form a chain of actuators and shafts extending along the span of the wing. A power drive unit (PDU) connected to the inboard end of the chain provides motive power for driving the actuators to selectively extend or retract the flight control surfaces.
Because control surfaces such as flaps or slats significantly alter the lift producing characteristics of the wings, and because it is desirable to control the weight of the aircraft, the actuation systems have had features for reacting to problems such as jamming or failure of one of the actuators or drive shafts in the aircraft flight control system. The actuators have included, for example, a force limiting device that limits the amount of force that can be applied to the control surface and further causes stalling of the PDU to prevent movement of the other control surfaces.